Field of the Invention
The present invention relates to nanostructured materials for use in rechargeable energy storage devices such as lithium batteries, particularly rechargeable secondary lithium batteries, or lithium-ion batteries (LIBs). The present invention includes materials, components, and devices, including nanostructured materials for use as battery active materials, and lithium ion battery (LIB) electrodes comprising such nanostructured materials, as well as manufacturing methods related thereto. Exemplary nanostructured materials include silicon-based nanostructures such as silicon nanowires and coated silicon nanowires, nanostructures disposed on substrates comprising active materials or current collectors such as silicon nanowires disposed on graphite particles or copper electrode plates, and LIB anode composites comprising high-capacity active material nanostructures formed on a porous copper and/or graphite powder substrate. The present invention includes active material nanostructures and methods of manufacturing related to nanostructure processing, including electrochemical deposition (ECD) of silicon nanostructures on LIB anode active materials and current collectors. The present invention also relates to LIB materials including binders, electrolytes, electrolyte additives, and solid electrolyte interfaces (SEIs) suitable for use in LIB anodes comprising silicon and graphite materials, as well as components, devices, and methods of manufacturing related thereto.
Background of the Invention
Conventional LIBs suffer from poor capacity, energy density, and cycle life. Silicon (Si) has been studied extensively as an active material in LIBs due to its appealing characteristics, including its high theoretical specific capacity of ˜4200 mAh/g for lithium (Li) and its low discharge potential. Si has slightly higher voltage plateau than that of graphite, so it has attractive safety characteristics. Si is abundant and inexpensive material, and lithiated Si is more stable in typical lithium-ion battery electrolytes than lithiated graphite.
Despite the attractive characteristics of silicon, commercialization attempts to utilize Si as an active material have been unsuccessful. Several factors contribute to this lack of success, including the lack of suitable methods available for mass producing high-quality Si-based anodic materials, the lack of solutions to address the detrimental consequences of the high volumetric expansion and contraction of Si during lithiation and delithiation, and the lack of solutions to address the low intrinsic conductivity of Si. There exists a need for high-quality, cost-effective Si-based anodic materials for LIBs; materials, composites, and LIB components for use in Si-based LIBs; methods for producing and utilizing such materials, and related LIB devices and components and methods related thereto.
Traditional lithium batteries, including lithium-ion batteries (LIBs), typically comprise an anode, a cathode, a separator material separating the cathode and anode, and an electrolyte. The anode of most commercially available LIBs generally includes a copper foil current collector coated with a mixture of graphite powder and a binder material. The cathode of most commercially available LIBs generally includes an aluminum foil current collector coated with a lithium transition metal oxide based cathode material. Traditional LIB anodes include intercalation-based active materials, such as graphite, which have limited charge capacity and cannot meet the rising demands of higher energy density, higher power density, and longer battery lifespan. Extensive research and development efforts have been dedicated to lithium (Li) alloying active materials for LIBs, such as silicon (Si), which has a theoretical charge capacity of ˜4200 mAh/g. However, several issues have prevented commercialization of silicon-based LIBs.
Thin film Si active materials have been the subject of recent investigation for use in LIBs, but thin film Si lacks the high surface area of nanostructures and is susceptible to pulverization upon high volumetric flux. Low-temperature methods for producing Si nanomaterials have included ball-milling Si to produce Si powder active materials, but such methods result in low-quality Si particles having large, inconsistent particle sizes and low crystallinity.
Production of high-grade silicon nanostructures for LIB active materials typically involves chemical vapor deposition (CVD) or wet chemistry techniques, including high-temperature catalyzed growth of silicon nanostructures such as silicon nanowires. For example, such methods are disclosed in U.S. Pat. Nos. 7,842,432 and 7,776,760, U.S. patent application Ser. Nos. 12/824,485 and 12/783,243, and U.S. Provisional Patent Application Ser. No. 61/511,826, the disclosures of each of which are herein incorporated by reference in their entireties. Typical methods of manufacturing silicon-based nanostructures include using gold (Au) as a catalyst material for catalyzed growth of silicon nanostructures at high temperatures. Gold is widely used as a catalyst material due to its high chemical stability, but since gold is expensive, it is not an ideal material for use in mass production of silicon-based materials. Copper catalyst materials have been proposed as an alternative to gold for catalyzed growth of silicon nanostructures for LIB active materials, as disclosed in U.S. Provisional Patent Application Ser. No. 61/511,826, the disclosure of which is incorporated by reference herein in its entirety.
There exists a need for cost-effective methods of mass-producing high-quality silicon-based materials suitable for use in LIBs, particularly for use as active materials in LIB anodes. Further, there exists a need for low-temperature processes which do not require the use of catalyst materials for production of such silicon nanostructures. Further, there exists a need for improved control over the physical and chemical characteristics of such silicon nanostructures during production to ensure proper device performance. Further, there exists a need for high quality silicon active materials having improved bond strength with the substrate to which the silicon is attached.
Additionally, there exists a need for materials, components, devices, and methods which accommodate the high volumetric expansion and contraction of silicon which occurs during lithiation and delithiation. Problems associated with the high volumetric changes of silicon include active material degradation, unpredictable changes to the active material structure, exfoliation of anodic materials from the current collector, loss of conductivity, SEI degradation, inadequate or excess SEI formation, and undesirable side reactions due to excess silicon active sites. These side effects contribute to unpredictable changes in the battery materials and system, thereby causing large hysteresis in the battery system's operation characteristics.
The present invention provides solutions to these and other problems, including solutions which provide control over the battery material and component characteristics both during production and throughout the multiple charge cycles and in the various conditions to which the battery is exposed. There exists a need for LIB binder materials, electrolyte materials, and SEI materials or layers suitable for use in LIB anode materials comprising Si active materials, particularly Si and graphite active materials.